Blinking of eyes is medically known as being deeply related to the inner state of human beings. Therefore, it is considered that the inner state of a human being may be understood by detecting blinking from images and videos and analyzing the features.
As a technology for detecting blinking, there is a technology of detecting the difference between a face motion vector and an eye (eyelid) motion vector between images, and determining that blinking has been performed when the detected vector difference is downward and greater than a predetermined value (see, for example, patent document 1).
Patent document 1: Japanese Laid-Open Patent Publication No. 2001-43382
The blink detection technology is widely applied, such as to digital cameras. It is assumed that the digital camera has high resolution and a high frame rate when taking pictures, and that the target is still and staring at the camera.
However, in the field of user monitoring, there is demand for performing blink detection even when images are captured at low resolution, in consideration of cases where the target is moving and the performance of a low-cost camera.
When blink detection is performed with an image taken at low resolution, the following problems arise. In a low-resolution image, the feature points of the eye area tend to deform/disappear. The reason why feature points disappear and deform is that when the eyelids are closed, the black part of the eye and the white part of the eye disappear, and the color pattern in this area changes.
As a result, the motion vectors in the eye area become inaccurate, which leads to inaccuracy in the eye motion vectors expressing the motion of the eye. That is to say, there are cases where the eye motion vector does not appropriately express the motion in the eye area.
Furthermore, the motion amount of the face is greater than the motion amount of the eyes. In the case of a low-resolution image, a minor error margin in calculating the face motion vector may be the same as the motion amount of blinking. In the conventional technology, blinking is determined based on the difference between an eye motion vector and a face motion vector, and therefore erroneous detections may be made with images in which the face moves.
That is to say, in the blinking determination of the conventional technology, the motions are expressed as one representative value (the difference between the face motion vector and the eye motion vector). Therefore, if the representative value includes an error, erroneous detections or failures in making detections may occur.